1. Field of the Invention
The invention relates to method and apparatus for detecting the leakage of coolant into the jacket of a nuclear-reactor fuel rod, by means of a member disposed within the jacket, which reacts to the coolant, thereby deforming the jacket to provide a visible indication of leakage.
2. Description of the Prior Art
Presently known apparatus and method for detecting coolant leakage into the jackets of nuclear reactor fuel rods comprise the detection of phenomena not apparent by inspection of the jackets. For example, a cup-shaped ferromagnetic body is arranged within the generally tubular jacket of a nuclear reactor fuel rod and a sphere is arranged therein. The sphere is suspended on a wire attached to a cap of the jacket. The ferromagnetic, cup-shaped body is filled with a material which disintegrates under the action of coolant and which, when not exposed to the coolant, prevents the ferromagnetic body from being released by the sphere.
The filler material is in the shape of a rod and encloses the sphere. As the free edge of the ferromagnetic body is bent inward, a bond results between the body, the filler material and the sphere. The bond is destroyed if coolant enters, because of the disintegration of the filler material by the coolant. The ferromagnetic body then falls and comes to rest on the surface of the nuclear fuel contained within the jacket. The change in position of the ferromagnetic body can be detected from outside the jacket by suitable measuring means, without the necessity of changing the position of the fuel rod.
The known apparatus and method, however, can be used only in fuel rods which have a sufficiently long distance for the ferromagnetic body to fall. Furthermore, the cost of the measuring apparatus is relatively high. A measurement can be falsified by other magnetic elements incorporated within the reactor, for instance, spacers or the like.